Electrophoretic Properties of Colloidal Dispersions of Monodisperse Zinc Sulfide: Effects of Potential-Determining Ions and Surface Oxidation

Surface Chemical Analysis and Electrokinetic Properties of Synthetic Spherical Mixed Zinc–Cadmium Sulfides

“…They were performed at the samples. Similar studies have been reported on other metal sulfides such as galena (8) or ZnS (9).…”

“…It could be expected that the pH corresponding to the isoelectric point (pH iep ) of the mixed sulfides M3, M8, and M12 would be in between those two values. Figure 5 shows the variation of m e with the pH of the NaCl 10 (8,9), obtained with galena and ZnS particles, convincingly demonstrated that the larger the oxidation degree of the surface the higher the pH iep shift to more basic values. In order to check if this argument also holds for our mixed sulfides, Fig.…”

“…Interestingly, sample M12, the least oxidizedand richest in Zn 2/ -shows a pH iep very close to that characteristic of ZnS spheres (9).…”

“…sions kept in the dark). These figures also include the conductivity of colloidal spheres of ZnS (320 nm in diameter, Apparently, at this relatively high temperature the sulfides precipitate rather fast (excess S 20 is rapidly generated be-and specific surface area of 40 m 2 /g) and CdS (780 nm; 4.6 m 2 /g) (9,16). The pH of the suspensions was between cause of the decomposition of TA), thus hindering the formation of a Zn-Cd mixed lattice.…”

“…The effect on the electrophoretic mobility of ZnS or CdS particles of ions forming part of the crystal structure (Zn 2/ , Cd 2/ , S 20 , or HS 0 , for pH £12) of the particles has been thoroughly studied in the literature (9,12,(18)(19)(20)(21). Since our mixed samples might respond, in their electric surface properties, to any of such ions, it seems of interest to consider how m e changes in solutions containing them.…”